The Infested Mind

Why humans fear, loathe, and love insects

Delusional Infestations and Real Suffering

When false beliefs about insects lead to true misery

Delusory parasitosis may cause sufferers to mutilate their skin.
Delusory parasitosis may lead to intense scratching, scraping, cutting, and use of caustic or toxic chemicals.
(image by Tomer Scheib)

In my last entry, I discussed insect-based hallucinations and illusions.  A delusion is an even more insidious phenomenon which entails not just a mistaken perception but an erroneous and persistent belief.

A classic account of delusory parasitosis involved an elderly couple who, in an effort to rid themselves of imaginary insects, boiled their bedding and clothing daily, baked their pillows and cushions, burned their couch and bed, and sprayed themselves with DDT. 

Such extreme behaviors often begin with four symptoms.  First is the “matchbox sign” named for the proclivity of sufferers to present an expert with a matchbox (or other container) said to hold the offending insects but has only household detritus.  Next, the patient offers vivid accounts of the insects and their origins, which vary depending on the individual’s background and experiences. Third, the sufferer’s belief is unshakeable to the point that family members come to adamantly support, and thereby reinforce, the delusion.  Finally, individuals have damaged their skin through scratching, cutting, and applying toxic chemicals. 

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Delusory parasitosis has been found to originate in various ways, often being rooted in a previous, disturbing encounter with insects such as an infestation of cockroaches, fleas, or lice.  If the origins of delusory parasitosis are complicated, the demographics of the disorder are consistent.  The typical patient would be a 65-year old woman of average intelligence.  Due to the ‘contagious’ nature of the delusional state, in 10 to 25% of the cases, the condition is shared by family members in a phenomenon called folie partagée, meaning “shared madness”.

Although delusional disorders are rare, many psychologists believe that delusory parasitosis is far more common than the literature would suggest.  Many, perhaps most, extension entomologists and pest control operators know of people who appear to have the disorder.  The person making initial contact is advised to neither confirm nor challenge the claim of being infested, but to gently and firmly direct the individual to a medical professional.

Without help, the condition rarely resolves itself.  Therapists have a range of options, none of which are sure fire treatments.  Psychotherapy and psychoanalysis work in some cases, but most studies favor Cognitive Behavioral Therapy, which entails having the patient systematically reunite emotional feeling with rational thought.  In severe cases, psychoactive drugs are used to alleviate acute symptoms.

All of this assumes that the patient is delusional—and sometimes people are infested with barely discernible arthropods. As such, consultations among entomologists, dermatologists and mental health professionals are optimal.  Such collaborations might have diagnosed two of the strangest cases of delusory parasitosis, which became spectacular examples of how a passionate belief can sway even the critical process of scientific peer review.  I’ll explore these twisted tales in my next blog…

Jeffrey Lockwood, Ph.D., is Professor of Natural Sciences and Humanities at the University of Wyoming and author of The Infested Mind.

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